* Add sort by option to node selector
Allow the final decision of a selected node to be based on different
sorting options rather than just random.
Add a `sysload`, `cpuload`, `rooms`, `clients`, `tracks`, and
`bytespersec` sorting options to select the appropriate room when
multiple are suitable for the chosen selector.
Add tests for sysload sort_by option
Closes: #598
* NodeSelector: rename "random" selector to "any"
Since the selector introduces limits but the final selection is now
based on the sort by value, the random selector name does not make
sense. Rename this selector to "any" to accurately reflect that it will
select any available no with no additional selection limits.
Allow the old setting "random" to point to the new selector name, but
print a deprecation warning message.
